Magnetron cathode structure



May 21, 1963 R. w. FIYOLSOM MAGNETRON CATHODE STRUCTURE Filed June 28 FIG.|

FIGZ

INVENTOR.

ROBERT W. FOLSOM ATTORNEY United States Patent 3,636,831 MAGNETRON CATHODE STRUCTURE Robert W. Folsom, Waltham, Mass., assignor to Comtelr, Inc, a corporation of Delaware Filed June 28, 1961, Ser. No. 120,423 8 Claims. ((31. 31539.51)

The present invention relates generally to magnetron oscillator devices and, in particular, to a new and unique cathode structure.

The magnetron is a well-known device for the generation of radio frequency energy in the microwave spectrum. One of the many problems associated with the usage of these devices in radar transmitters is the overall life which is critically dependent upon the source of continued emission of the electrons. Since the procurement costs of magnetrons is quite high, failure of a relatively small component of the overall structure, such as the cathode-emitter, warrants consideration of a means for reactivation by replacement of the cathode structure. Such replacement, however, is complicated by the fact that all applicable devices are highly evacuated and depend for their operation on the degree of vacuum existent within the tube envelope.

It is, therefore, a primary object of the present invention to provide a new and unique replaceable cathode structure for magnetron oscillator devices.

A further object of the invention is the provision of a replaceable cathode structure which assures maintenance of the high degree of vacuum necessary for the proper functioning of the tube.

A feature of the present invention resides in a wholly integral and separable cathode assembly which when inserted into the tube envelope assures a vacuum-tight seal at the point of contact. This vacuum seal is attained without resort to soldering, brazing or other prior art vacuum sealing techniques. An advantage of the structure is that costly tubes need not be discarded as a result of being inoperative due to heater burn out, short-circuiting of heater elements, cathode poisoning or lack of sufficient emissive material. The faulty cathode structure may be removed and a completely new one installed in a minimum of time without special tools being required and the overall tube may be re-evacuated to the high vacuum desired.

Other objects, features and advantages will be apparent after consideration of the following detailed specification taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a detailed cross-sectional view of an illustrative embodiment of the invention;

FIG. 2 is an enlarged cross-sectional view of the cathode structure of the present invention; and

FIG. 3 is a perspective view of the embodiment prior to insertion into the magnetron tube envelope.

Referring to FIG. 1 the magnetron oscillator illustrated is of the so-called packaged-type incorporating external magnets 11 and 12 to generate microwave energy at a specific fixed frequency. An anode member 13 of the multi-segmented type defines a plurality of resonant cavities surrounding a central passageway 14. Outer pole pieces 15 and 16 abut opposite ends of the anode member 13 to facilitate the direction of the magnetic field into the interaction space defined by the resonant cavities. The combined pole pieces and anode member define the overall tube envelope which is generally evacuated by means of exhaust tubulation 17 joined to pole piece 15.

Energy generated by the magnetron tube may be coupled by means of a short section of coaxial line 18 joined to the anode member vanes 19 by means of legs 20. A dielectric enclosure 21 surrounds the outer end of the coaxial line 18 and is joined to the tube envelope by means of a metallic cup 22 to thereby vacuum seal this end of the 3,090,891 Patented May 21, 1963 tube envelope. Cooling fins 23 mounted on the tube envelope, permit cooling by means of the direction of forced air on the lateral surfaces thereof.

The opposite end of the tube envelope supports a cathode electrode assembly which is easily inserted and removed in accordance with the teachings of the present invention. This assembly will now be described with attention being directed to FIGS. 2 and 3. A tubular extension 24 is joined to the outer end of pole piece 15. The inner Walls of extension 24 are counterbored to provide a chamfered seat 25. In addition an inner threaded section 26 is provided adjacent to the outer end of this extension. I next provide an integral and unitary sub-assembly comprising an elongated tubular support member 27 having a substantially spool-shaped configuration disposed at one end thereof. This section, indicated by the numeral 28, is coated with a layer 29 of an emissive material commonly employed in the art. If desired, this end of the support member may be adapted for one of the dispensertype cathode-emitters wherein a porous tungsten metal is impregnated with the emissive material. Axially disposed within the support member 27 is a heater element 30 together with the electrical connection means 31. The outer end of support member 27 is vacuum sealed by means of a glass-to-metal seal 32. The conventional high voltage connection means include a terminal connector 33 joined at this end of the support member 27.

A coaxially disposed hollow sleeve member 34 is joined at an intermediate point to support member 27 by means of a dielectric member 35, such as glass or ceramic bead. Sleeve member 34 is desirably fabricated of a soft deformable metal such as copper, and is provided with a flared flange 36 at one end thereof. In addition, a convoluted section 37 is provided to thereby relieve any strains which might possibly damage dielectric seal 35.

Whenever replacement of the cathode electrode structure is desired the inoperative cathode may be removed and a completely new assembly inserted into the axial passageway 38 which communicates with the anode. cen-.

tral passageway 14. The cathode electrode assembly may be inserted until the fiared flange 36 of sleeve member 34 contacts the chamfered seat 25. A threaded plug 39 is then introduced into extension 24 with its nose portion 40 contacting flange 36. Since this portion is tapered to mate with flange 36 and seat 25, rotation of the plug will result in compression of the soft copper material. This will result in a substantial cold metal-to-metal seal which will effectively retain the vacuum condition of the overall tube. The threaded portion 26 as well as the glug threads may be carefully controlled to assure a good After insertion of the new cathode electrode assembly the overall magnetron tube may be re-activated by conventional vacuum pumping techniques and exhaust tubulation 17 will be tipped-off and sealed as at 41.

As a result of the teachings of this invention a simple and efficient means is provided for the continued operation of the high cost magnetron tubes. Prior art magnetrons not embodying the tubular extension 24 may be easily converted and adapted with such a member at a minimum of cost. Replacement cathode assemblies can always be maintained readily available and can be inserted with a minimum of skilled labor required. While a specific embodiment of t e invention has been described herein, various modifications or alterations will occur to persons skilled in the art without departing from the scope thereof. It is intended, therefore, that all matter contained in the above specification or shown in the accompanying drawings shall be interpreted in a manner consonant with the definition of the invention in the appended claims.

What is claimed is:

l. A magnetron oscillator comprising a multi-segmented anode resonator defining a central passageway, pole piece members of a magnetic material abutting opposite ends of said resonator, a tubular extension member joined tothe outer end of one of said pole piece member-s, said tubular extension member defining a passageway communicating with said central passageway and wall structure defining a seat disposed therein, a unitary cathode electrode assembly removably disposed within said tubular extension member, said cathode electrode assembly comprising a tubular support member having disposed at one end thereof an emissive material, a hollow sleeve member'coaxially disposed about an intermediate point of said support member and being joined thereto by a vacuum-tight seal, said sleeve member defining a flange portion adapted to mate with said seat when the latter is contacted and means for retaining under compression the contacting surfaces of said flange and seat to thereby eifect a cold metal-to-metal vacuum seal.

2. 'A magnetron oscillator comprising a cylindrical multisegmented anode resonator defining a central passageway, a plurality of magnetic. metallic pole piece member joined to opposite ends of said resonator, a metallic tubular extension member joined to the outer end of one of said pole piece members, said tubular extension member defining a passageway communicating with said central passageway and wall structure defining a chamfered seat disposed therein, a unitary cathodeelectrode assembly adapted to be inserted within said passageway, said cathode electrode assembly comprising an elongated metallic tubular support member having disposed at one end thereof a coating of an emissive material, a hollow metallic sleeve member coaxially disposed about an intermediate point of said support member and being joined thereto by a dielectric seal, said sleeve member defining a flared flange portion adapted to mate with said seat when the latter is contacted and means for retaining under compression the contacting metallic surfaces of said flange and seat to thereby effect a cold metal-to-metal vacuum seal.

3. A magnetron oscillator according to claim 2 wherein said sleeve member defines a convoluted section adjacent to the flange portion.

4. A magnetron oscillator according to claim 2 wherein wall structure adjacent to the outerend of said extension member passageway defines an internal threaded section.

5. A magnetron oscillator according to claim 2 wherein said retaining means comprise a threaded plug member extending into said extension member passageway with its inner end contacting said flange and seat.

6. A cathode electrode assembly for electron discharge devices of the magnetron type comprising an elongated hollow tubular member defining at one end thereof an area of an emissive material, a heater element disposed within said tubular member and being joined thereto by a vacuum retaining seal, a hollow sleeve member of a soft deformable metal coaxially disposed about an intermediate point of said tubular member and being joined thereto by a vacuum retaining seal, said sleeve member defining a tapered flange portion and an intermediate convoluted section, and high voltage electrical connection means disposed at the non-emissive end of said tubular member.

7. In a magnetron oscillator device having a cylindrical metallic envelope with a hollow tubular extension member joined at one end thereof to provide a passageway communicating with the interior of said envelope, a cathode electrode assembly adapted to be inserted into said passageway, said cathode electrode assembly comprising an elongated hollow tubular member having disposed atone end thereof a coating of an emissive material, a heater element disposed within said tubular member and being joined thereto by a dielectric-to-metal' seal, a hollow sleeve member of a soft deformable metal coaxially disposed about an intermediate point of said tubular member and being joined thereto by a dielectricto-metal seal, said sleeve member defining a tapered flange portion and in intermediate convoluted section and means for retaining said cathode assembly within wall structure defined said passageway to provide UNITED STATES PATENTS Krause Nov. 17, 1942' Spencer Sept. 6. 1949 

1. A MAGNETRON OSCILLATOR COMPRISING A MULTI-SEGMENTED ANODE RESONATOR DEFINING A CENTRAL PASSAGEWAY, POLE PIECE MEMBERS OF A MAGNETIC MATERIAL ABUTTING OPPOSITE ENDS OF SAID RESONATOR, A TUBULAR EXTENSION MEMBER JOINED TO THE OUTER OF ONE OF SAID POLE PIECE MEMBERS, SAID TUBULAR EXTENSION MEMBER DEFINING A PASSAGEWAY COMMUNICATING WITH SAID CENTRAL PASSAGEWAY AND WALL STRUCTURE DEFINING A SEAT DISPOSED THEREIN, A UNITARY CATHODE ELECTRODE ASSEMBLY REMOVABLY DISPOSED WITHIN SAID TUBULAR EXTENSION MEMBER, SAID CATHODE ELECTRODE ASSEMBLY COMPRISING A TUBULAR SUPPORT MEMBER HAVING DISPOSED AT ONE END THEREOF AN EMISSIVE MATERIAL, A HOLLOW SLEEVE MEMBER COAXIALLY DISPOSED ABOUT AN INTERMEDIATE POINT OF SAID SUPPORT MEMBER AND BEING JOINED THERETO BY A VACUUM-TIGHT SEAL, SAID SLEEVE MEMBER DEFINING A FLANGE PORTION ADAPTED TO MATE WITH SAID SEAT WHEN THE LATTER IS CONTACTED AND MEANS FOR RETAINING UNDER COMPRESSION THE CONTACTING SURFACES OF SAID FLANGE AND SEAT TO THEREBY EFFECT A COLD METAL-TO-METAL VACUUM SEAL. 